1. Field of the Invention
The present invention relates to an optical waveguide circuit component incorporating an optical waveguide circuit and a method of manufacturing the same, and, more particularly, to a planar light wave circuit component with a small polarization-dependent loss and a method of manufacturing the same.
2. Description of the Related Art
A planer light wave circuit (PLC) component is well known as an optical waveguide circuit component. As an example of a PLC component, an optical waveguide device is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2003-43272.
In this device, the pattern of an optical waveguide circuit is formed on a silicon wafer, and a cover layer called a lid (an auxiliary plate in Jpn. Pat. Appln. KOKAI Publication No. 2003-43272) is fixed onto the silicon wafer formed with an optical waveguide circuit.
An optical waveguide circuit is formed on a substrate processed by etching or the like. In general, a core is provided as a lower clad layer on a quartz glass plate, for example, and the core is covered by an upper clad layer.
A lid provided on a substrate protects the substrate, and provides a connection surface for an input/output connector that is optically connected to a PLC component, facilitating the connection.
Jpn. Pat. Appln. KOKAI Publication No. 2001-74972 discloses a structure to fix an optical waveguide circuit board to a holder by using an elastic adhesive.
As described in Jpn. Pat. Appln. KOKAI Publication Nos. 2003-43272 and 2001-74972, in the optical circuit board provided with an optical waveguide circuit, an auxiliary member such as a lid is fixed by using an adhesive. An adhesive is softened and applied to the bonding surface of a substrate or lid. When the adhesive is hardened, the lid is fixed to the substrate. An adhesive itself shrinks when hardened, and generates stress internally. This internal stress is transmitted not only to the lid, but also the optical circuit board, generating a similar internal stress in the optical circuit board. As a result, one of the longitudinal mode (TE mode) and transverse mode (TM mode) of an optical beam transmitted in the light waveguide circuit is greatly attenuated, and the ratio is changed. Namely, a polarization-dependent loss is increased.
Particularly, in an optical distributor, for example, an optical directional coupler having one input and two outputs, a polarization-dependent loss of an input beam generated during transmission in the distributor is increased.
If an atmospheric temperature of an optical waveguide circuit component is changed, internal stress is generated in a substrate according to the coefficient of thermal expansion, and a polarization-dependent loss is generated in an optical beam transmitted in the optical waveguide circuit as described above, because the coefficients of thermal expansion of the substrate and adhesive are different.
The above-mentioned problem is concerned with an optical distributor, but not limited to an optical distributor. Similar problems arise in other optical components having an optical waveguide circuit, for example, an optical branch circuit.